feedline and dipole question, as well as request for input....

[KD6VXI]

Quick question for the antenna guru's out there.

I just laid the new all band dipole out (125 feet of #10 stranded and still in the insulation, basically got two runs of 125 feet of #10 house stranded), and have yet to string it up off the ground, as I have a feeders question.

I have another 100 feet, but need about 10, to get in the house.  I'm on the third story, so I'm going to hang the dipole off the house, about 5 to 10 feet, using a 2X4 to keep it away from the eave's.  I need to know the spacing of the feeders to get 450 ohms!  I want to start the spacing at the dipole feedpoint, so I can't "string it up", so to speak, until I know what spacing of #10, stranded, house wiring (with the insulation on it) will give me 450 or so ohms (I want it in the measurable range of my MFJ 259).

I am located in Tehachapi, Ca.  The dipole is about 100 feet to 125 feet HAAT at the apex, sloping down to about 30 on one side, and 50 on the other tip.  Configuration is a SLIGHT V, the southern leg giving me good coverage towards the NE area, the northern tip being almost ideally centered E/W. 

I live on a gentle slope, so getting out towards the pacific will be a challenge, to say the least, as I still have another 150 to 500 feet of mountain behind me, but the dipole will be about 100 feet in front of the mountain (so I figured, in a traingle config, the dipole would be equallaterally laying (in average) 100 feet above and in front of the ground.  Should make for a decent DX and local coverage antenna.

I plan on just drilling spaced holes for the feedline to come into the house, balanced all the way to the tuna (which will be built as soon as I can source the caps, junkbox is completely dry at the moment)....  I figured this would keep the thing as balanced as possible.  I'm going to explore the K1JJ tuna first, as it's seems to be the tuna of choice.

Rig at the moment is just a lowly FT857, but has a few mods to sound decent on AM....  ALC been up'ped, carrier brought down where there is slight positive shift under modulation, capable of 100+ percent positive, etc.  It's not a plate modulated box by any means, but into the load thus far, it sounds as good as the microphone will allow. 

The future dictates dedicated solid state rigs for each band, I already have a solid state modulator designed, tested, built and in use...  It's a simple device, capable of modulating a 20 watt carrier, but passes nearly from DC to daylight, and I use the computer for all audio shaping and processing.

Anywho, long story short, I need the feedline spacing for the 10 gauge common stranded house wiring, so I can build the center support and start building the feedline for the dipole.  I'm thinking 18 feet of feedline would be ideal, as that would give me total of 268 feet, giving me coverage of 1.6 meg and up.

I have a bit of time to get this all up in the air, as we don't have any tests for almost two months in the area, and with the lowly tech license, I can't use most of the bands, but I figure this gives me time to build the tuna!  And the MFJ allows me to ensure it's all working before the license comes!

(the station is legal limit, I have two amps, a pair of 3-500s and a single 3-1000, although they are both 3 meg and above amps.....  I'll be having a 160 capable amp in the near future if needs dictate it).  I also have the space to erect a bev...  20 acres of farm land, I'm situated against a gentle hill to the back of me, approximately 100 feet behind me.....  BUT, I have about a thousand feet in front of the main house to erect antennas...  I've swept the area for noise sources, and haven't found a single electric fence, while driving around (using the ATAS 120 antenna as a reference, although it SUCKS below 40 mtrs, it at least gave me some RX).

Thanks, in advance, and I look forward to hearing back...  I wanna get this thing strung up and get to listening.  NEVER had the wire or space to erect a full size dipole for anything other than maybe 15 meters for listening before, I'm figuring a full size 160 will be an amazing improvement, at least for RX for the next few weeks!

--Shane
KD6VXI

[KB2WIG]

Try a bit over 2 1/2 inches; thar's a graph in most ARRgL handbooks...

klc

[Jim KF2SY]

1.) Don't get hung up on exact spacing for feedline.  Just keep it consistantly spaced.  Even the commercial "450 ladderline" is not exactly 450 ohms.  The 14 ga. version of the stuff is more like, IIRC about 420 ohms.
 
2.)  Build the K1JJ antenna tuner.  Is works terrific, beleive all the good things you here about it.
Some say it can cure bad breath, dandruff and athletes foot, but I can't vouch for those claims.
 
Good luck and have fun...

Jim

[Steve - WB3HUZ]

For air:

Z_o = 276 * log(2D/d)


Where D is the center-to-center spacing between wires in the same units as d, and d is the outer diameter of the conductors.

[kc2ifr]

Hmmmmm,

I have used the crappy brown stuff...14ga......and now I use home brew feedline  #10 solid copper wire spaced about 6 inches outside the house and 4 inches inside the house to the ant tooner. If the antenna is going to be used on different bands, the 450 ohm Z goes out the window. I have absolutely NO problems on all bands. The ant tooner is link coupled and built to handle gobs of power.
Dont get hung up on 450 ohms.........its NOT that important.

Bill

[W2DU]

Bill is correct--don't get hung up on 450 ohms, because the tuner doesn't care. Use spreaders of any convenient length. In pre-WW2 days we used #12 wire spaced 6" with manufactured ceramic spreaders. Some ceramic spreaders were 3" long. The 6" spacing achieved a characteristic impedance of around 600 ohms, which was pretty much of a standard then. Whatever the spacing you use, when the tuner is adjusted for 1:1 at the input, the feedine is matched to both the tuner and the antenna.

Walt, W2DU

[kc2ifr]

One more quick point.....DO NOT USE A TOONER WITH A 4to1 balun on the out put...........use a link coupled tooner...the 4to1 is crap.
Bill

[KD6VXI]

Bill is correct--don't get hung up on 450 ohms, because the tuner doesn't care. Use spreaders of any convenient length. In pre-WW2 days we used #12 wire spaced 6" with manufactured ceramic spreaders. Some ceramic spreaders were 3" long. The 6" spacing achieved a characteristic impedance of around 600 ohms, which was pretty much of a standard then. Whatever the spacing you use, when the tuner is adjusted for 1:1 at the input, the feedine is matched to both the tuner and the antenna.

Walt, W2DU

Kinda what I figured.... 

I was looking at 450 ohms more because it's in the measurable range of my VNA....  The 259 only goes to 600 or so ohms before it says "Ain't happnin, friend".  I'll be happy with 6 inch spacing.

I'm sure 6 inch spacing can handle multiple kilowatts as well.

Also, thanks for the information you've shared through the years.  You tha man, as they say!

--Shane

[KD6VXI]

One more quick point.....DO NOT USE A TOONER WITH A 4to1 balun on the out put...........use a link coupled tooner...the 4to1 is crap.
Bill

As one who tends to get heavy fisted with a ceramic powered hit-me-stick, I learned long ago that baluns are junk....  'Cept for the coaxial coil, and I usually put a stack-0-beads on that as well.  (interesting, the coaxial coil is a choke, not a balun, so I still say, baluns = junk).

I'm going to put the K1JJ tuna togetha, (nice engrish), but the junkbawx is lacking at the moment.  Copper tubing is easy to find, but I have zero caps available atm.

I figured it would be best to start with the longest slice of wire I could, hence the 160 dipole for all bands, with a short feedline.

Thanks, for the input, as well.

--Shane

[Steve - WB3HUZ]

Excellent. You have the makings of a very nice antenna system there. Good luck with it and hope to hear it on the air soon!

One more quick point.....DO NOT USE A TOONER WITH A 4to1 balun on the out put...........use a link coupled tooner...the 4to1 is crap.
Bill

As one who tends to get heavy fisted with a ceramic powered hit-me-stick, I learned long ago that baluns are junk....  'Cept for the coaxial coil, and I usually put a stack-0-beads on that as well.  (interesting, the coaxial coil is a choke, not a balun, so I still say, baluns = junk).

I'm going to put the K1JJ tuna togetha, (nice engrish), but the junkbawx is lacking at the moment.  Copper tubing is easy to find, but I have zero caps available atm.

I figured it would be best to start with the longest slice of wire I could, hence the 160 dipole for all bands, with a short feedline.

Thanks, for the input, as well.

--Shane

[N3DRB The Derb]

do yourself a favor and buy some of these to use for your coil connections once you start putting the fire to the wire. JS clip leads wont hack it.


http://www.bwantennas.com/coils/coilclip.htm

[K1JJ]

Hi Shane,

Yep, you can't go wrong building a Vu-Tuna! 

As for vacuum variables, that's the way to go.... there's some on e-Bay now. You want a 500pf (max) at 7kv or higher.  Get a turns counter too.

http://cgi.ebay.com/Vacuum-Variable-Capacitor-KP1-4-10-500-pF-10kV-BONUS_W0QQitemZ260397306255QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item260397306255&_trksid=p3286.c0.m14&_trkparms=72%3A1234%7C66%3A2%7C65%3A12%7C39%3A1%7C240%3A1318%7C301%3A0%7C293%3A1%7C294%3A50

Or do a search on eBay for "vacuum variables".  There is also a Russian dealer who sells them on the web.


You are building the antenna system correctly and you'll find you will be loud on all bands and gain a lot of satisfaction building and using your own tuner. It's an education in itself finding the taps and learning how the tuner works on the various bands.  You will find that openwire feedline is not critical as long as you use good materials and reasonable diameter wire. The flat top size is not critical either as long as you can match it and it's not shorter than a 1/4 wavelength long on the lowest band. (no shorter)   The most important factor is getting the flatop up as straight, flat and high as possible with the feedline coming down at a perfect right angle.  Inverted vee is OK, but a flat dipole or near flat is better.  If you get it to 60' or higher, you will be very happy with performance on all bands, especially with your HAAT there.

You might add a 6V flashlight type bulb on each feeder leg (in the shack) to measure RF balance. Solder two leads to a bulb and solder it onto ONE leg with the lead spacing about 3-4" or so on the one wire. Do this to each leg. Tune up the tuner and put just enuff RF in so that each bulb BARELY lights. You can then play with the taps of the feedline on the main coil to get perfect balance - the same brightness for each bulb. This will help compensate for real world imbalances in the installation.  The eye is very sensitive to brightness levels when the bulb is barely lit.  An RF current meter in each leg will do the same thing for you.

BTW, bear in mind that with a 160M center fed dipole, on 40M you will have a cloverleaf four lobe pattern. This means you will have a big null broadside front and rear.  ie, Where the 80 and 160M patterns were strong figure eights on the broadside, you will be pissweak on 40M in those same directions.  By adding a set of 40M legs at the same feedpoint, you can again have a nice, broad, figure eight on 40M. I assume you are putting the antenna up in you favored directions broadside - and 40M is now a very important band.

Good luck.

T

[k4kyv]

do yourself a favor and buy some of these to use for your coil connections once you start putting the fire to the wire. JS clip leads wont hack it.


http://www.bwantennas.com/coils/coilclip.htm

Wow!  Thanks for the link.  I didn't think anyone made those any more.

[ve6pg]

..bill...ur tooner...does it tune 160?., and what is the diameter of the coil?....and.....how many turns is the link coil, on the inside?..
...tim..

..sk..

[kc2ifr]

Tim,
My antenna is a 75 meter dipole and yes the tooner does tune it on 160 even though the tooner is a parallel tooner. On 160 the tuning is VERY sharp but it works fine. In the picture u can see where the coil is tapped using alligator clips. I dont have to move the taps between 75 and 160, just adjust the input and output caps for 0 swr.

The coil is an old varometer (spelling) with the primary on the inside of the secondary and it can be moved in or out although I leave it in.

I will count the turns on the primary and let ya know what they are and Ill measure the size.

Bill   

[KD6VXI]

BTW, bear in mind that with a 160M center fed dipole, on 40M you will have a cloverleaf four lobe pattern. This means you will have a big null broadside front and rear.  ie, Where the 80 and 160M patterns were strong figure eights on the broadside, you will be pissweak on 40M in those same directions.  By adding a set of 40M legs at the same feedpoint, you can again have a nice, broad, figure eight on 40M. I assume you are putting the antenna up in you favored directions broadside - and 40M is now a very important band.

Good luck.

T

Tom,

Thanks for the input, it is MUCHO appreciated.  I hadn't searched VV's in awhile, they are going DOWN in price, it seems.  Great day for me!

Directly above the feedpoint of the dipole, I have a rescued 31' tall aluminum monopole from a CB antenna.  I had figured to use the dipole and the vertical on 40-10, probably feeding the vertical against the dipole shorted to ground as the "radials" for the thing.

Looking at the site yesterday again, I think I'm more along the lines of about a 60 degree included angle on the thing.  I can't get it perfectly flat, but reasonably so.  Maybe someday I can add another leg to it, and create a "steerable" V-Beam. 

Wire = cheap, compared to aluminum.  With the tuna, all things are possible !

--Shane

[ke7trp]

Good advice here Shane.

If I was you, I would just go to http://www.trueladderline.com/   and just order the length of this open wire line you need and be done with it.

I ran the 450 ohm solid line and then the 450 ohm 18G stranded line. Both worked well. The main drawback is that if there is any moisture or rain, your tuning changes big time. 

I ordered this open wire line and this problem is gone. I have a big increase on 40 meters and 20 is flat across the band. 

If you insist on using the heavy 10G wire then just use 4 to 6 inch spacers. It wont make any real difference. I suggest this stuff because its cheap and the guy ships in a reasonable time frame. If you want it NOW, Let me know. I have 120FT of it sitting in the spare room. I can Fedex it to you and then you can replace it later.

Make sure right now that you understand the need for a Balanced tuner with this stuff.  I use the KW matchbox. I think I have a spare Johnson 250 tuner here if you need to use it. The link coupled tuner is what you want. Using a roller/balun tuner is going to be a HUGE decrease in performance. I tested this back to back from KW to my big palstar.

The big drawback of the Johnson tuner is the lack of 160.. 

I think you will be shocked at how good this antenna is going to work.. We can talk on 40 all day long, 80 and 160 at night no problem.

Clark

[KA2QFX]

Quoting W2DU;

don't get hung up on 450 ohms, because the tuner doesn't care. Use spreaders of any convenient length.

Well, you couldn't get any better advice than that!  Specifically, the line impedance will likely never see 450 ohms at either end, so the tuner will take care of the mismatch regardless.  The only concern you might have is line spacing when the voltages get very high, where the antenna feedpoint becomes a voltage node. ei: the antenna is an even number of 1/4 waves on each side, like 40 meters.  In which case a few inches of feedline spacing should be sufficient and a GOOD antenna center insulator is critical.

BTW: I LOVE BALUNs, UNUNs and all manner of transmission line transformers for differnet applications.  They work GREAT, but only when applied properly. All my resonant antennas are fed with broadband TLT baluns/ununs with EXCELLENT results.  Non resonant antennas do not match up to specfied impedance baluns and only a simple choke (ferrite loaded or otherwise) can be used to  eliminate feedline radiation.  But to say baluns are junk is just ridiculous.

Regards,
Mark

[ke7trp]

Baluns have there place. But not on a multiband antenna.

Clark

[Steve - WB3HUZ]

Unless it's a log periodic or a triband beam or a fan dipole or ......

Baluns have there place. But not on a multiband antenna.

Clark

[ke7trp]

yeah.. I meant using open wire line but not coax fed not resonant.

Clark

[flintstone mop]

Yea Shane
What others have given here is a reliable recipe for a working antenna / tuna combo that works very well with many folks. It's not a system you can hang a piece of test equipment on. It makes the transmitter happy to see 50 ohms and you're on the air.
I hope we can talk on the air soon

Fred

[KD6VXI]

Good advice here Shane.

If I was you, I would just go to http://www.trueladderline.com/   and just order the length of this open wire line you need and be done with it.

I ran the 450 ohm solid line and then the 450 ohm 18G stranded line. Both worked well. The main drawback is that if there is any moisture or rain, your tuning changes big time. 

I ordered this open wire line and this problem is gone. I have a big increase on 40 meters and 20 is flat across the band. 

If you insist on using the heavy 10G wire then just use 4 to 6 inch spacers. It wont make any real difference. I suggest this stuff because its cheap and the guy ships in a reasonable time frame. If you want it NOW, Let me know. I have 120FT of it sitting in the spare room. I can Fedex it to you and then you can replace it later.

Make sure right now that you understand the need for a Balanced tuner with this stuff.  I use the KW matchbox. I think I have a spare Johnson 250 tuner here if you need to use it. The link coupled tuner is what you want. Using a roller/balun tuner is going to be a HUGE decrease in performance. I tested this back to back from KW to my big palstar.

The big drawback of the Johnson tuner is the lack of 160.. 

I think you will be shocked at how good this antenna is going to work.. We can talk on 40 all day long, 80 and 160 at night no problem.

Clark

Clark,

I have to design for near-arctic conditions.  I run 10 ga. because it will hold up, and I need at least 6 inch spread, because I can have 4 inches of ice on the elements.  HENCE the reason I'm keeping my feedling to such a short length.

www.n6nb.com is about 500 feet higher than me.  It's great for views (I can see from Disneyland to the glow of Sacramento with binocs), but in the winter, when an ice storm sets in, I've had many things go wrong.

31 foot tall radiator from the vertical was found about a eighth mile away, parts of it scattered amongst the permafrost, etc.

I have steel core copper coming from the ute company, but it's SO heavy, I doubt I'll be using it for much...  BUT, it's free, so I'll take it. 

I made up the line and everything, then got hit with registration on the truck, so caps take a back seat for another month.  No tuner in the radio, so I can listen for a bit (need the ticket upgraded as well).

I'll post some pictures somewhere of the ice storm stuff from the last two years and make a pointer.  Literally, I've had a 20 to 40 degree lean on my antennas, I gave up completely on Yagi antennas of aluminum here, it's a killer price-wise.  The wire v-beam is my friend, although not steerable with many conventionable means.

The only vertical that really holds up here is made from the same aluminum that Jay builds that 12 through 6 meter antenna monoband vertical you hated so much with (and I found the problem, the matching network was built as designed, and backwards...  A friend here had the same problem, and we fixed it reversing the "twin trombone" matching elements).  And I believe his are going for near 400 dollars or more now.  Mostly all in materials (I've seen the cost of the antennas vs shipped price).

--Shane